Microstructure Design And Energy Storage Performance Of PMMA-based Composite Dielectric

Dielectric capacitor is one kinds of the important energy storage and conversion devices,which are widely used in the fields of high voltage transmission system,new energy vehicle and electromagnetic catapult weapon.Compared with batteries and supercapacitors,dielectric capacitors are favored because of their advantages of high power density,fast charge and discharge,and good operation stability.Among them,polymers with linear polarization properties（such as polymethyl methacrylate,PMMA）have relatively low polarization loss and high energy storage efficiency,but their low relative dielectric constant results in low energy storage density.In addition,the charge injection from the electrode to the dielectric under high-field conditions is prominent,causing the increase of conductance loss and serious deterioration of energy storage performance.Based on this,this article aims to improve the energy storage performance of PMMA dielectric films through structural design,and provide a reference for the research of high-performance polymer-based energy storage dielectric.In this paper,PMMA was selected as the polymer matrix,and high dielectric constant barium strontium titanate nanofibers（Ba Sr Ti O₃ NFs,denoted as BST NFs）were used as the filling phase to prepare dielectric films by tape casting method.The PMMA-based composite dielectric system was constructed by changing the doping content of the filler phase and combining with surface modification technology,and its microstructure,dielectric properties,breakdown characteristics,polarization characteristics and energy storage performance were systematically characterized and tested.Studies had shown that as the doping content of BST NFs increased,the dielectric constant and polarization intensity of composite dielectric gradually increased,and the breakdown field strength gradually decreased.When the applied electric field intensity was 500 k V/mm,the energy storage density of 1 vol.%BST/PMMA composite dielectric was 10.6 J/cm³,which was 1.16 times that of pure PMMA film,and the charge-discharge efficiency was 77%.In addition,it was found that when BST modified with Si O₂（denoted as BST@S）was selected as the filling phase,which did not significantly improve the breakdown field strength and energy storage performance of composite dielectric.In order to suppress the conductance loss of composite dielectric under high electric field conditions and further improve the energy storage performance of the PMMA-based composite dielectric,this paper proposed to use magnetron sputtering technology to grow a wide band gap Si O₂ thin insulating layer on the upper and lower surfaces of the PMMA dielectric film in situ.By changing the sputtering time to control the growth thickness of the Si O₂ insulating layers,the influence of the thickness of the Si O₂ layers on the surface structure and energy storage performance of the composite dielectric was systematically studied.The research showed that when the sputtering time was 2 hours and the thickness of the Si O₂ thin layer was about 240 nm,the composite dielectric exhibited excellent energy storage performance.When the applied electric field was 520 k V/mm,the energy density of the Si O₂/PMMA/Si O₂ composite dielectric was 14.5 J/cm³,which was 1.59 times that of the pure PMMA film,and the efficiency reached 87.4%.With the same sputtering process,the energy storage density of 1 vol.%BST/PMMA composite dielectric grown with Si O₂ thin layers was increased the most,the maximum discharge energy density reached 15.7 J/cm³,and the charge-discharge efficiency was 79.8%.